e.g. I missed the last bus. I could do nothing but stay in the village for the night.

We have no choice but to wait.

6). 主语部分含有动词do的一定形式时，作主语补语的不定式可以省去to, 也可保留to。

e.g. The thing to do is (to) clear the road.

7). 在“let +动词”组成的固定词组中。

e.g. Hold it tight and don’t let go.

Exercises:

1. Sir Denis, who is 78, has made it known that much of his collection ______ to the nation.
A、has left
B、is to leave
C、leaves
D、is to be left
2. It is not unusual for workers in that region _________.
A、to be paid more than a month later
B、to be paid later than more a month
C、to pay later than a month more
D、to pay later more than a month
3. The ancient Egyptians are supposed _________ rockets to the moon.
A、to send
B、to be sending
C、to have sent
D、to have been sending
4. They are going to have the serviceman __________ an electric fan in the office tomorrow.
A、install
B、to install
C、to be installed
D、installed
5. There is a man at the reception desk who seems very angry and I think he means _________ trouble.
A、making
B、to make
C、to have made
D、having made
6. I’d rather read than watch television; the programs seem __________ all the time.
A、to get worse
B、to be getting worse
C、to have got worse
D、getting worse
7. Could you find someone________？
A、for me to play tennis with
B、for me to play tennis
C、play tennis with
D、playing tennis
8. The pressure ________causes Americans to be energetic, but it also puts them under a constant emotional strain.
A、to compete
B、competing
C、to be competed
D、having competed
9. You will want two trees about ten feet apart, from _____ to suspend your tent.
A、there
B、them
C、which
D、where
10. ________ a teacher in a university, it is necessary to have at least a master’s degree.
A、To become
B、Become
C、One becomes
D、On becoming
11. That was so serious a matter that I had no choice but ____ the police.
A、called in
B、calling in
C、call in
D、to call in
12. If I had remembered ________ the window, the thief would not have got in.
A、to close
B、closing
C、to have closed
D、having closed
13. Mr. Johnson preferred _____ heavier work to do.
A、to be given
B、to be giving
C、to have given
D、having given
14. The teacher didn’t think we needed _____ how important the exam was.
A、to be told
B、to tell
C、having told
D、being told
15. The piano weighs three hundred pounds, so it is too heavy ________.
A、for me to move
B、to move by me
C、for me not to move
D、not to move by me
16. Mary likes listening to the radio much better than _______ television.
A、to watch
B、watch
C、watching
D、watched
17. When the police broke the door open they found the young man _______badly wounded on the floor.
A、to lie
B、lying
C、being lying
D、lieing
18. The last man _______ the sinking ship was the captain.
A、left
B、leaves
C、to leave
D、to be leaving
19. It is not unusual for workers in that region____.
A、to be paid more than a month late
B、to be paid later than more a month
C、to pay later than a month more
D、to pay late more than a month
20. ______ a teacher in a university, it is necessary to have at least a master’s degree.
A、To become
B、Become
C、One becomes
D、On becoming